JPH11320622A - Pressurized fluid injection structure of hollow injection molding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve stable injection of a pressurized fluid such as gas by forming a flow path in the opposite faces between the inner circumferential face of a sleeve pin and the outer circumferential face of a center pin by relatively positioning them. SOLUTION: In a structure of a pressurized fluid injection part constituted of a center pin 11 and a sleeve pin 2, protrusions 12 are provided at three portions which are equally spaced apart on the circumference of the center pin 11, and a clearance forms a gas path 6 which is formed between the outer circumferential face of the center pin 11 and the inner circumferential face of the sleeve pin 2. The clearance is mechanically fixed in accordance with the height of the protrusions 12 provided in the outer circumference of the center pin 11, thereby ensuring the steady gas path and keeping the constant gas pressure at all times over all the directions around the center pin 11, so as to achieve the gas injection.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressurized fluid injection part structure of a hollow injection molding apparatus for forming a hollow portion in a molten resin in a mold cavity by press-fitting a pressurized fluid such as gas. In particular, the present invention relates to a pressurized fluid injection unit structure suitable for manufacturing a molded product having no warpage or local defect (sink) in appearance.

[0002]

2. Description of the Related Art Conventionally, in this type of so-called gas assist molding, the structure of a gas injection portion as a pressurized fluid is roughly classified into two types.

[0003] One is a check valve system described in Japanese Patent Application Laid-Open No. 64-14012, which prevents a backflow of molten resin and presses the check valve with gas pressure during gas injection and injection. Blows off the molten resin filled to the stop valve position,
A hollow portion is formed by passing a gas through the molten resin.

However, in this check valve system, as the number of moldings increases, the molten resin affects the operation of the check valve,
The malfunction of the check valve may occur. In addition, it is necessary to raise the temperature of the sleeve containing the check valve with a heater or the like so that the molten resin that is in contact with the check valve does not solidify. ,
This has made the injection and injection stability of the gas difficult.

Another method is disclosed in Japanese Patent Application Laid-Open No. Hei 5-17766.
No. 7, etc., which is a pin method, in which a clearance is provided between the center pin and the sleeve pin so that the resin does not flow backward, and gas is introduced into the molten resin inside the molded article through the clearance. is there.

[0006] The pin system has advantages over the check valve system in that there are no problems such as malfunction and no need to heat the tip of the pin. However, when actually confirming how the gas enters the inside of the molded product, it has been confirmed that the gas introduction position is not constant due to the difference in the molding shot.

[0007]

By the way, such a plastic hollow molded article by the gas assist molding method is as follows.
It is expected to reduce the “warpage deformation” which is a characteristic of plastic molded products, as compared with plastic molded products obtained by ordinary injection molding. Other advantages of the gas assist molding method and the hollow molded article include a reduction in material cost due to the formation of the hollow portion and an improvement in local appearance defects (such as sink marks). However, on the other hand, there is a new problem that the dimensional stability of a molded product is impaired due to the difference in the way gas enters the molten resin to be plasticized. In particular, the stability of the gas pressure from the inlet, which is an inlet for introducing gas into the molten resin, is greatly affected by the way gas enters (how a hollow portion is formed in the molten resin) and the dimensional stability of molded products. It is becoming apparent that it is having an effect.

In the conventional gas injection portion structure, since the center pin and the sleeve pin are simply fitted, the gap between the outer peripheral surface of the center pin and the inner peripheral surface of the sleeve pin, that is, the gas flow path is formed inside the sleeve pin. It changed due to the eccentricity of the center pin, and the gap as the gas flow path could not be formed uniformly on the outer periphery of the center pin, and the gas entry was not stable. Also, as a conventional gas injection unit structure, although there are those that mention the backflow of resin, gas leakage as a pressurized fluid, the speed of recovery of the gas, etc.,
Nothing mentioned the stability of the gas entry.

[0009] In the conventional pin method, how the gas enters the molten resin is confirmed as shown in FIGS. 1, 2 and 3. In these figures, 1 is a center pin, 2 is a sleeve pin fitted with the center pin 1, 3 is a mold forming a cavity of a molded product, and 4 is a molten resin filled in the cavity. 5 is a gas introduced into the molten resin 4. In the case of such a simple fitting structure of the center pin 1 and the sleeve pin 2, as shown in FIG. 2 and FIG. As a result, the gas 5 cannot be uniformly injected. In addition, every time the pins 1 and 2 are disassembled and cleaned during maintenance of the mold 3, their eccentric directions change, and stable molding cannot be performed.

As described above, the center pin 1 is eccentric with respect to the sleeve pin 2, and as a result, gas cannot be efficiently injected as desired. That is,
The clearance formed between the center pin 1 and the sleeve pin 2 varies irregularly depending on the fitted state, and it was not possible to grasp in which direction the gas 5 easily flows. Furthermore, since the actual flow of the gas 5 is not stable, the injection direction of the gas 5 cannot be controlled, and stable molding is difficult.

On the other hand, the gas 5 tends to flow to a low thickness portion in the molten resin 4. That is, in the molten resin 4,
The gas 5 easily flows to a place where the temperature is high and the density is low.

Normally, the molten resin 4 flowing into the cavity is rapidly solidified by the temperature of the mold 3 with respect to the surface layer in contact with the mold 3, whereas the center of the cavity in the plate thickness direction is increased. As for the layer, its solidification rate is slow. In the molten resin 4, a portion where the gas 5 flows most easily is a molten portion in the center layer in the thickness direction of the cavity. In order for the gas 5 to reach the melting portion, the gas 5 needs to break through the solidified layer. Therefore, a gas pressure enough to break through the solidified layer is required, and a gas pressure higher than the gas pressure required for the flow in the molten layer is originally required.

If the flow during the injection of the gas 5 becomes non-uniform, the gas pressure becomes non-uniform, and it becomes impossible to supply a gas pressure sufficient to allow the gas 5 to break through the solidified layer, and the flow direction becomes uneven. It becomes a rule. Therefore, there is a possibility that the gas 5 reaches the molten layer via a completely indeterminate path, or that the gas 5 does not sufficiently reach the molten resin 4 and gas leakage or the like occurs. In such a situation, stable filling of the gas 5 into the molded article is not guaranteed, and the stability of the quality of the molded article cannot be maintained. Furthermore, the gas injected and injected from the clearance between the pins 1 and 2 makes various movements,
Products of stable quality cannot be molded.

An object of the present invention is to provide a pressurized fluid injection unit structure of a hollow injection molding apparatus capable of stably injecting a pressurized fluid such as gas.

[0015]

The structure of the pressurized fluid injection part of the hollow injection molding apparatus according to the present invention is characterized in that a molten resin in a mold cavity is passed through a flow path formed between a sleeve pin and a center pin inside the sleeve pin. In the pressurized fluid injection unit structure of a hollow injection molding apparatus for injecting pressurized fluid into, between the inner peripheral surface of the sleeve pin and the outer peripheral surface of the center pin,
It is characterized in that they are positioned relatively to each other, and a flow path forming portion for forming the flow path is provided between their facing surfaces.

The pressurized fluid injection part structure of the hollow injection molding apparatus according to the present invention is characterized in that a pressurized fluid is injected into a molten resin in a mold cavity through a flow path formed between a sleeve pin and a center pin inside the sleeve pin. In the pressurized fluid injection part structure of the hollow injection molding apparatus for injecting a fluid, at least one of the inner peripheral surface of the sleeve pin and the outer peripheral surface of the center pin fitted to each other, and extends in the axial direction, A groove for forming a flow path is provided.

The pressurized fluid injection part structure of the hollow injection molding apparatus according to the present invention is characterized in that a pressurized fluid is injected into a molten resin in a mold cavity through a flow path formed between a sleeve pin and a center pin inside the sleeve pin. In a pressurized fluid injection unit structure of a hollow injection molding apparatus for injecting a fluid, a groove having an end facing the flow path is provided at a tip of the center pin.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIGS. 4 to 7 are explanatory diagrams of a first embodiment of the present invention, and FIGS. 8 to 12 are explanatory diagrams of modifications thereof.

4 and 5, reference numeral 11 denotes a center pin. The center pin 11 of the present example has a cross-sectional shape perpendicular to the axial direction as shown in FIG. 5, and is provided with three protrusions 12 at equal intervals on the circumference. Further, similarly to the above-mentioned conventional example, 2 is a sleeve pin, 3 is a mold forming a cavity, 4 is a molten resin, and 5 is a gas as a pressurized fluid. 6 is the center pin 1
1 is a gas flow path formed between the protrusion 12 provided on the outer periphery of the sleeve pin 1 and the inner surface of the sleeve pin 2. The protrusion 12 extends in the longitudinal direction of the center pin 11, and the tip thereof contacts the inner surface of the sleeve pin 2.

In such a gas inlet structure of this embodiment, the clearance as the gas flow path 6 formed between the outer peripheral surface of the center pin 11 and the inner peripheral surface of the sleeve pin 2 is equal to the outer circumference of the center pin 11. Is mechanically fixed by the height of the projections 12 provided on the upper surface. Therefore, a constant gas flow path is secured, and the gas 5 can be injected while always maintaining a uniform gas pressure in all directions around the center pin 11.

As a result, the stability of gas injection, which is the main object of the present invention, is improved. In other words, a stable flow of the gas 5 is always maintained, and the gas pressure from the same path is always guided into the molten resin 4 every shot, in the same state, so that a hollow molded product with stable quality and a stable molded product size Is obtained. Further, since the gas injection path is stabilized, stable gas injection can be performed even if a gas leak occurs due to an inappropriate setting of a gas nozzle for injecting the gas 5 or an inappropriate setting of the nozzle diameter. By doing so, it is possible to easily optimize the gas nozzle setting location and the nozzle diameter in order to eliminate the gas leakage.

FIG. 6 is a flowchart for explaining the procedure of the hollow injection molding operation by gas injection.

First, in step S1, the cavity is filled with the molten resin 4 to be plasticized. After the filling of the molten resin 4 is completed, step S is performed in a short time.
The injection and injection of the second gas 5 is performed. The timing of the injection of the gas 5 is important and is called an injection delay time, and it is desirable that the timing is almost the same after the filling of the molten resin 4 is completed. Since the molten resin 4 solidifies immediately after flowing into the cavity, if the injection timing of the gas 5 is missed, the injection of the gas 5 becomes insufficient unless the gas pressure is extremely increased. Would. By setting the injection timing of the gas 5 optimally, stable molding with the low-pressure gas 5 becomes possible.

In the next step S3, the pressure of the gas 5 is maintained in the hollow portion of the molten resin 4. If the sealing ability of the gas injection part is low, gas leakage is likely to occur. In the next step S4, the gas 5 is recovered. Cooling of the resin 4 is performed in steps S3 and S4. In step S3, a gas holding time for maintaining the quality of the molded product is required.

After the above process, the molded product is taken out in step S5.

In the present embodiment, a gas injection nozzle constituted by the center pin 11 and the sleeve pin 2 having a sectional shape as shown in FIG. 5 is used. Center pin 11
The height (width of the gas flow path) of the protrusion 12 formed on the outer periphery of was set at 25 μm.

Using such a gas injection portion structure, FIG.
Table 1 shows the conditions of the gas supply system when the molded article W1 shown in FIG.

[0029]

[Table 1]

As a result of using the gas injection nozzle having such a structure, the injection path of the gas 5 into the molten resin 4 is stabilized, and the molded product can be always formed into a stable and good appearance. The leak has gone.

8 to 12 show a combination structure with a center pin 13 having a triangular cross section, FIG. 9 shows a combination structure with a center pin 14 having a rectangular cross section, and FIG. 10 shows a center pin having a hexagonal cross section. 15 and can be combined with a center having various cross-sectional shapes such as a polygonal cross-section. The point is that the gas flow path 6 may be formed so as to define a clearance. FIG. 11 shows three projections at the outer peripheral portion.
FIG. 12 shows a combination structure with a center pin 16 having six protrusions 19 at regular intervals on the outer periphery of the center pin. It is also possible to combine with a center pin or the like having the protrusions at equal intervals, and it is only necessary to form the gas flow path 6 so as to define the clearance.

The hollow portion of the sleeve pin has a circular cross section, the inner peripheral surface thereof has a circular shape, and the cross section of the center pin side projection has a semicircular, triangular or quadrangular shape, and the height of the projection is 5 mm. It is preferable to set it to 30 μm.

(Second Embodiment) FIGS. 13 to 15 show:
Explanatory drawing of a second embodiment of the present invention, FIGS.
Is an explanatory diagram of the modification.

Originally, hollow injection molding has an advantage in that it can be applied to the requirement of a thick part of a molded article whose shrinkage is larger than that of the periphery, that is, the shape of the molded article which requires advanced molding and a long cooling time. is there. As a molded product having a typical shape into which gas as a pressurized fluid is injected, there is a molded product W2 in which a plate-shaped main body is provided with a rib W2-1 for reinforcing strength as shown in FIG. . In the case of this molded product W2,
In general, a gas flow path is formed in the portion of the thick rib W2-1, and the direction in which the gas flows is uniquely determined by the shape. If gas can be injected efficiently in the direction in which it is desired to flow, it is possible to efficiently penetrate the solidified layer of the molten resin with the minimum gas pressure and avoid gas loss, etc. Become. In FIG. 13, W2-2 is a gas inlet, W2-
The dotted line with 3 indicates the gas filling status.

In the present embodiment, stable gas injection into the molten layer of the molten resin is realized.

FIGS. 14 and 15 are explanatory views of a gas inlet structure used for molding the molded article W2 as shown in FIG. 13. The same parts as those in the above-described embodiment are denoted by the same reference numerals and will be described. Omitted.

Reference numeral 21 denotes a center pin, and grooves 22 extending in the axial direction are provided at two places on the circumference that come into contact with the inner peripheral surface of the sleeve pin 2. The gas passage 6 is formed between the groove 22 and the inner surface of the sleeve pin 2. As described above, the clearance as the gas flow path 6 formed between the outer peripheral surface of the center pin 11 and the inner peripheral surface of the sleeve pin 2 is the groove 22 provided on the outer periphery of the center pin 11.
Is mechanically fixed depending on the depth and width (cross-sectional area) of the wire. Therefore, the gas 5 can be injected only in the gas injection direction. Therefore, unnecessary gas leakage is eliminated, and gas pressure can be applied only in the direction in which gas is to be flowed efficiently, and the gas 5 penetrates through the solidified layer of the resin 4 with the minimum gas pressure and flows into the molten resin 4. It became possible to inject.

The center pin 21 as shown in FIGS.
The depth of the groove 22 was set to 25 μm in the gas injection nozzle constituted by the sleeve pin 2 and the molded product W2 in FIG.
The growth flow path was stabilized, and the molded product W2 could always be molded into a stable and good appearance, and sudden gas leakage was eliminated.

In the modified examples shown in FIGS. 16 to 18, in order to form the molded product W3 shown in FIG.
As shown in FIG. 8, a gas injection nozzle constituted by a center pin 23 and a sleeve pin 2 was used. W in FIG.
3-1 is a rib of the molded product W3, W3-2 is a gas inlet, W
The dotted line portion 3-3 indicates the gas filling status. Also, a rib W3-1 is provided on the outer periphery of the center pin 23 of this example.
The grooves 24 are formed at three places corresponding to the longitudinal direction. Then, a clearance as the gas flow path 6 is formed between the outer peripheral surface of the center pin 23 and the inner peripheral surface of the sleeve pin 2. In the case of this example, the depth of the groove 24 was set to 30 μm.

As described above, the molded product W3 of FIG. 16 is molded using the gas injection port structure of FIGS. 17 and 18, and as a result, the growth flow path of the gas 5 in the molten resin 4 is stabilized, and the molded product W3 Thus, stable and good appearance molding was possible, and sudden gas leakage was eliminated.

The cross-sectional shape and depth of the groove provided in the center pin can be appropriately changed. The depth of the groove is preferably 5 μm to 30 μm.

(Third Embodiment) FIG. 19 is a schematic structural view of an entire injection molding apparatus to which the present invention can be applied, and FIGS.
1 is an explanatory view of a conventional example, FIGS. 22 and 23 are explanatory views of a third embodiment of the present invention, FIG. 24 is an explanatory view of a first modification thereof, and FIGS. It is explanatory drawing of the modification of.

First, in the overall configuration shown in FIG. 9, C is a cavity formed by the mold 3. 1 is a center pin, 2 is a sleeve pin circumscribing the center pin 1, and these constitute a gas injection part. 7
Is a clearance formed between the cut surface of the center pin 1 and the inner surface of the sleeve pin 2. The gas introduced into the hollow portion 8 from the gas supply device through the passage 9 is injected into the molten resin filled in the cavity C through the clearance 7.

In the conventional pin method shown in FIGS. 20 and 21, reference numeral 4 denotes a molten resin filled in the cavity C;
Is a gas introduced into the resin 4. Gas 5 from a passage 9 is introduced into the molten resin 4 through a clearance 7 formed between the sleeve pin 2 and the center pin 1. FIG. 21 is a plan view of a gas injection portion constituted by the conventional pins 1 and 2 of FIG. The tip of the conventional center pin 1 is simply flat.

In such a conventional pin method, when performing gas injection, there are two problems in flowing the gas 5 through the molten resin. One is that there is a loss in the process in which the gas 5 reaches the molten layer of the resin 4. Another is that the gas 5 flows in the molten resin 4 independently from both sides of the center pin 1.

Here, the gas 5 easily flows to a place where the pressure in the molten resin 4 is low. That is, the gas 5 easily flows to a place where the temperature is high and the density is low in the resin 4. Normally, the molten resin 4 flowing into the cavity C rapidly solidifies due to the temperature of the mold 3 with respect to the surface layer in contact with the mold 3, whereas the central layer in the thickness direction of the cavity C is formed. , Its solidification rate is slow. In the molten resin 4, a portion where the gas 5 flows most easily is a molten portion in the center layer in the thickness direction of the cavity.

However, in the conventional case shown in FIGS. 20 and 21, it is necessary for the gas 5 to break through the solidified layer before the gas 5 reaches the melting portion. Therefore, a gas pressure enough to break through the solidified layer is required, and a gas pressure higher than the gas pressure required for the flow in the molten layer is originally required. If the flow during the injection of the gas 5 becomes non-uniform, the gas pressure becomes non-uniform, so that the gas 5 cannot supply a gas pressure enough to break through the solidified layer, and the flow direction becomes irregular. Would. Therefore, there is a possibility that the gas 5 reaches the molten layer via a completely indeterminate path, or that the gas 5 does not sufficiently reach the molten resin 4 and gas leakage or the like occurs. In such a situation, stable filling of the gas 5 into the molded article is not guaranteed, and the stability of the quality of the molded article cannot be maintained. Further, the gas injected and injected from the clearance between the pins 1 and 2 makes various movements, so that a product of stable quality cannot be formed.

The third embodiment of the present invention shown in FIGS. 22 and 23 and the modified examples shown in FIGS. 24, 25 and 26 realize stable gas ejection at low pressure.

First, the third embodiment of the present invention shown in FIGS.
In the embodiment, a groove 10 is formed at the tip of the center pin 1 facing the molten layer. The groove 10
Are formed so as to be orthogonal to the cut surface of the center pin 1 for forming the clearance 7. FIG.
It is a top view of such pins 1 and 2. Further, the clearance 7 is set to 10 μm to 50 μm.

In the case of this example, the gas 5 passing through the clearance 7
Is the resin in the groove 10. A sleeve wall 2A is located on the inner surface of the sleeve pin 2 facing the end of the groove 10, and the sleeve wall 2A
The gas 5 is prevented from being guided in a direction opposite to that in the groove 10. The thickness of the resin 4 at the position of the groove 10 is larger than that of the resin 4 located at another portion of the center pin 1, particularly at another portion near the groove 10. That is, the thickness of the plastic part at the position of the groove 10 is greater than the other plastic parts in the vicinity. Accordingly, the molten layer of the plastic portion facing the groove 10 is thicker, and the high-temperature molten layer is located closer to the clearance 7 serving as a gas injection port. Therefore, the gas 5 is guided toward the center of the center pin 1 from the periphery of the center pin 1 along the groove 10. Since the groove 10 communicates with both sides of the clearance 7, the gas 5 from both sides concentrates in the center direction and flows into the molten layer in a more stable state.

The effect of this is enormous. First,
Since the gas pressure can reach the molten layer at a low pressure, the consumption of the gas 5 can be small. In the case of the conventional method described above,
In order to break through the solidified layer, a certain high gas pressure is required, and if the gas pressure is close, sinking or the like occurs due to poor gas filling. Therefore, the consumption amount of the gas 5 was inevitably increased. Further, in the conventional method, if the gas pressure is set to a large value in order to solve such a problem, the gas path from when the gas 5 breaks through the solidified layer to reach the molten layer becomes unstable.

On the other hand, in the embodiment of the present invention, only a low gas pressure is required, and the gas path is limited. Therefore, in each shot, the gas 5 that has passed through the same gas path is guided into the molten resin 4 in the same state, and a hollow molded product and molded product dimensions of stable quality can be obtained. Furthermore, gas leakage is less likely to occur, and the injection of the gas 5 is stabilized. In the case of the conventional method, as shown in FIG. 20, the gas 5 is discharged outward from the pin 1 and passes through a position close to the sleeve pin 2, so that gas leaks from between the sleeve pin 2 and the mold 3. Was easy to happen. However, in the embodiment of the present invention, since the gas 5 is guided toward the center of the center pin 1, the possibility of gas leakage is extremely small.

Next, in a first modified example of FIG.
The same effect is obtained by projecting only the center pin 1 into the molten resin 4. Also in this case, the center pin 1
Groove 10 serves as a guide for gas 5. However, in the case of such a shape of the center pin 1, attention must be paid to the projecting position of the center pin 1 into the molten resin 4, and the projecting position is more than the center position of the basic thickness of the molded product. It is better to set it on the side, that is, on the lower side in FIG. That is, it is better to set the protruding portion of the front end of the center pin 1 in the range up to the center of the cavity C in the vertical direction in FIG. This has the advantage that the gas injection port is located near the molten portion of the resin,
This is because a hollow portion in the initial stage of gas introduction is formed in the molded product, and the advantage that the gas 5 is concentrated on the center from both sides and guided to the molten layer is impaired.

In the second modified example shown in FIGS. 25 and 26, the center pin 1 is made narrower, that is, the center pin 1 is shaped so that the center protrudes from the periphery, and the groove is formed. 10 are molded. The same effect is obtained in the case of this example.

It should be noted that the center pin 1 may be made of a material such as ceramic having a lower thermal conductivity than the sleeve pin 2 and the mold 3. Further, only the tip portion of the center pin 1 may be made of a material such as ceramic having a lower thermal conductivity than the sleeve pin 2 and the mold 3.

Further, by using the gas injection portion structure of the third embodiment of the present invention and its modification, the molded article W1 of FIG. 7 described above can be molded under the conditions of Table 1 described above.
It has become possible to lower the gas pressure. In the conventional structure, molding with a gas pressure of 100 kgf / cm ² or less was difficult, but a much lower gas pressure (80 kF / cm ² ) was used.
gf / cm ² or less).

(Others) In the above-described first embodiment and its modifications, instead of forming the center pin side into a polygonal cross section or providing a projection on the outer peripheral surface of the center pin,
Alternatively, the cross-sectional shape of the sleeve pin may be changed, or a protrusion may be provided on the inner peripheral surface of the sleeve pin. In short, it is only necessary to regulate the distance between the outer peripheral surface of the center pin and the inner peripheral surface of the sleeve pin so that a gas flow path can be formed in that portion. Insofar, a spacer is interposed between the center pin and the sleeve pin. It is also possible to make it. Further, the size, the number, the formation position, the form, and the like of the gas flow path can be set according to the application.

In the above-described second embodiment and its modifications, a groove may be provided on the sleeve pin side instead of or together with the center pin side. The point is that a gas flow path for guiding gas in a desired direction can be formed between the outer peripheral surface of the center pin and the inner peripheral surface of the sleeve pin. Further, the size, the number, the formation position, the form, and the like of the gas flow path can be set according to the application.

Further, by combining the above-described first and second embodiments and their modifications with the above-described third embodiment, gas can be more stably injected. In that case, it is desirable to match the position of the gas flow path formed between the center pin and the sleeve pin with both sides of the groove 10.

[0060]

As described above, according to the present invention, a pressurized fluid such as a gas can be stably injected. As a result, leakage of the pressurized fluid at the time of holding the pressurized fluid can be eliminated.
It is possible to reduce the consumption of the pressurized fluid and stabilize the quality of the molded product.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a pressurized fluid injection state in a conventional pressurized fluid injection section.

FIG. 2 is an explanatory diagram of a pressurized fluid injection state in a conventional pressurized fluid injection section.

FIG. 3 is an explanatory diagram of a pressurized fluid injection state in a pressurized fluid injection section of the present invention.

FIG. 4 is an explanatory diagram of a pressurized fluid injection state according to the first embodiment of the present invention.

FIG. 5 is a cross-sectional view of the center pin and the sleeve pin in FIG.

FIG. 6 is a flowchart for explaining a work procedure of hollow injection molding.

FIG. 7 is a perspective view of a specific molded product.

FIG. 8 is a cross-sectional view of a main part for describing a modification of the first embodiment of the present invention.

FIG. 9 is a cross-sectional view of a main part for describing another modification of the first embodiment of the present invention.

FIG. 10 is a cross-sectional view of a main part for describing still another modification of the first embodiment of the present invention.

FIG. 11 is a cross-sectional view of a main part for describing still another modified example of the first embodiment of the present invention.

FIG. 12 is a cross-sectional view of a main part for describing still another modified example of the first embodiment of the present invention.

FIG. 13 is a perspective view of a molded product that can be molded according to the second embodiment of the present invention.

FIG. 14 is a longitudinal sectional view of a main part according to a second embodiment of the present invention.

FIG. 15 is a cross-sectional view of a main part of the second embodiment of the present invention.

FIG. 16 is a perspective view of a molded product that can be molded according to a modification of the second embodiment of the present invention.

FIG. 17 is a longitudinal sectional view of a main part of a modification of the second embodiment of the present invention.

FIG. 18 is a cross-sectional view of a main part of a modification of the second embodiment of the present invention.

FIG. 19 is a schematic cross-sectional view of the entire injection molding apparatus to which the third embodiment of the present invention can be applied.

FIG. 20 is an explanatory diagram of a pressurized fluid injection state in a conventional pressurized fluid injection section.

FIG. 21 is a plan view of a center pin and a sleeve pin in FIG. 20.

FIG. 22 is an explanatory diagram of a pressurized fluid injection state according to the third embodiment of the present invention.

FIG. 23 is a plan view of a center pin and a sleeve pin in FIG. 22.

FIG. 24 is an explanatory diagram of a pressurized fluid injection state in a modified example of the third embodiment of the present invention.

FIG. 25 is a longitudinal sectional view of a main part of another modification of the third embodiment of the present invention.

FIG. 26 is a plan view of a center pin and a sleeve pin in FIG. 25.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Center pin 2 Sleeve 3 Mold 4 Molten resin 5 Gas 6 Gas flow path 10 Groove part 11,13,14,15,16,18,21,23 Center pin 12,17,19 Projection 22,24 Groove

Claims (16)

[Claims] 1. A pressurized fluid injection part structure of a hollow injection molding apparatus for injecting pressurized fluid into a molten resin in a mold cavity through a flow path formed between a sleeve pin and a center pin inside the sleeve pin. A flow path forming portion that positions the relative positions between an inner peripheral surface of the sleeve pin and an outer peripheral surface of the center pin and forms the flow path between the opposing surfaces is provided. The pressurized fluid injection part structure of the hollow injection molding device, which is characterized. 2. The sleeve pin has a hollow portion having a circular cross section, the center pin has a polygonal cross section located in the hollow portion of the sleeve pin, and the flow path forming portion has a polygonal cross section. The pressurized fluid injection unit structure of a hollow injection molding apparatus according to claim 1, wherein the pressurized fluid injection unit is formed by a corner of the center pin. 3. The hollow injection molding according to claim 1, wherein the flow path forming portion is a projection protruding outward from an outer peripheral surface of the center pin and in contact with an inner peripheral surface of the sleeve pin. Pressurized fluid injection unit structure of the device. 4. The hollow injection molding according to claim 1, wherein the flow path forming portion is a protrusion protruding inward from an inner peripheral surface of the sleeve pin and in contact with an outer peripheral surface of the center pin. Pressurized fluid injection unit structure of the device. 5. The pressurized fluid injection part structure of a hollow injection molding apparatus according to claim 3, wherein the projection has a semicircular cross section. 6. The pressurized fluid injection part structure of a hollow injection molding apparatus according to claim 3, wherein the projection has a triangular cross section. 7. The pressurized fluid injection part structure of a hollow injection molding apparatus according to claim 3, wherein the projection has a rectangular cross section. 8. The pressurized fluid injection part structure of a hollow injection molding apparatus according to claim 3, wherein said projection has a height of 5 μm to 30 μm. 9. A pressurized fluid injection part structure of a hollow injection molding apparatus for injecting pressurized fluid into molten resin in a mold cavity through a flow path formed between a sleeve pin and a center pin inside the sleeve pin. A hollow injection hole formed in at least one of an inner peripheral surface of the sleeve pin and an outer peripheral surface of the center pin to be fitted with each other, the groove extending in the axial direction to form the flow path. Pressurized fluid injection unit structure of molding equipment. 10. The groove has a depth of 5 μm to 30 μm.
The pressurized fluid injection unit structure of the hollow injection molding apparatus according to claim 9, wherein: 11. A pressurized fluid injection part structure of a hollow injection molding apparatus for injecting pressurized fluid into a molten resin in a mold cavity through a flow path formed between a sleeve pin and a center pin inside the sleeve pin. A pressurized fluid injection unit structure for a hollow injection molding apparatus, wherein a groove having an end facing the flow path is provided at a tip of the center pin. 12. The flow path according to claim 1, wherein a distance between an inner peripheral surface of the sleeve pin and an outer peripheral surface of the center pin is 5 μm to 5 μm.
The pressurized fluid injection part structure of a hollow injection molding apparatus according to claim 11, wherein the groove is formed with a clearance of 0 µm, and both ends of the groove face the flow path. 13. The pressurized fluid injection of a hollow injection molding apparatus according to claim 11, wherein a tip portion of the center pin protrudes into the mold cavity beyond the sleeve pin. Part structure. 14. A tip of the center pin projects from a direction perpendicular to a molding surface of the mold to a center of the mold cavity in a width direction. The pressurized fluid injection part structure of the hollow injection molding apparatus according to claim 13, wherein 15. The pressurized fluid injection part of the hollow injection molding apparatus according to claim 11, wherein a center part of the tip part of the center pin projects more than a peripheral part thereof. Construction. 16. The apparatus according to claim 11, wherein at least a tip portion of the center pin is made of a material having a lower thermal conductivity than the sleeve pin and a mold forming the mold cavity. 3. The pressurized fluid injection unit structure of the hollow injection molding apparatus according to 1.